1. Field of the Invention
The present invention relates generally to the field of photolithography masks. More particularly, the present invention relates to the field of photolithography mask inspection and analysis.
2. Description of Related Art
Images of a manufactured mask may be captured, inspected, and analyzed to help ensure a desired target pattern may be adequately printed using the mask. The inspection and analysis of a mask therefore help verify that integrated circuits (ICs) or similar objects manufactured using the mask will function. A mask may be inspected and analyzed, for example, to help verify critical dimension (CD) requirements have been met, to help identify any defects and contamination in the mask and assess their severity, and/or to help verify that the desired target pattern will be adequately aligned relative to underlying and overlying layers.
Some mask analyses require the availability of a reference image of an ideal or desired mask portion corresponding to the mask portion of the subject image to be analyzed. A die-to-die mask inspection tool, for example, generates a reference image by capturing light transmitted either through a similar portion on the same mask or through a reference die known to have no or negligible defects or contamination. A die-to-database mask inspection tool, for example, generates a reference image from digitized data of the design for the mask.
Where, however, a reference image cannot be generated or is otherwise unavailable, any mask analyses that use a reference image cannot be performed.
As one example, the Automatic Defect Severity Scoring (ADSS) technology of the Virtual Stepper® System developed by Numerical Technologies, Inc. of San Jose, Calif. may be used with a mask inspection tool to assess mask quality and the printability of mask defects. Because ADSS uses a reference image to perform one or more mask analyses, ADSS may not be used, for example, with a STARlight inspection tool provided by KLA-Tencor Corporation of San Jose, Calif. STARlight is a tradename used by KLATencor Corporation for an inspection tool that captures transmitted and reflected images of a portion of a mask to identify defects and contaminants. A STARlight inspection tool, however, does not generate any reference images.